1. Field of the Invention
The present invention relates generally to the field of security devices for buildings, and particularly for homes. More specifically the present invention relates to a door or window lock including a conventional slide chain mounted to the door or sliding window frame which engages a slot in a latch box mounted to the door or window perimeter frame. The latching box contains an alarm circuit which is activated by movement of the chain along the slot.
2. Description of the Prior Art
There have long been locks and alarm systems for preventing unauthorized entry into buildings. These have in some instances been integrated together so that breaking or lateral movement of a bolt triggers the alarm. A problem with these latter type of prior devices has been that they generally do not operate in concert with the conventional bolt assembly many people have on doors, which are conveniently operated with house keys. In these instances the alarm must be set, neutralized and deactivated in a separate operation from simply locking and unlocking the door, discouraging hurried people from using their alarm systems all of the time. Alternatively, in the few instances in which a generally conventional bolt assembly is used, deactivation of a triggered alarm can be complicated and difficult.
One such prior device is that of Gould, U.S. Pat. No. 2,825,777, issued on Mar. 4, 1958. Gould discloses a burglar alarm including a battery-powered electric alarm mounted on a door or window which is connected by a two-wire cable to a detector switch unit mounted on a door or window frame. The detector switch includes a toggle-pivoted and preferably dielectric detector element engaged with a window sash. The detector switch is a two-arm spring switch, with one arm being longer than the other and having the detector element pivotally mounted on its free end. The two-arms of the switch in contact until the detector element is engaged by the sash and moved to a horizontal position so that its mounting arm is sprung away from the other switch arm. A problem with Gould is that the two-wire cable interconnecting the wall and door or window mounted alarm portions offers no real resistance to opening the door or window, and such opening would rip the wires out of the switch and damage the unit.
Cashman, U.S. Pat. No. 4,124,847, issued on Nov. 7, 1978, reveals a door alarm system. Cashman includes a door switch mounted on the hinge side of a door which operates through the movement of a pivoting conductive arm within the switch, the arm free end being connected to the door frame or wall by a chain. The arm is spring biased to keep the circuit closed, and the chain overcomes the biasing when engaged while the door is closed. Opening the door while the chain engages the switch removes tension in the chain and creates chain slack, so that the arm pivots with the biasing of the spring to close the circuit and activate the alarm. A problem with Cashman is that the chain does not inhibit opening of the door and the latching or locking of the door must be accomplished as a separate step from setting the alarm.
Nakada, U.S. Pat. No. 4,205,305, issued on May 27, 1980, teaches a burglar alarm. Nakada includes a housing which contains a bell assembly and a battery compartment connected in series with a switch assembly. The switch assembly has a linearly movable element which can be displaced a predetermined threshold distance by a chain extending to a magnet temporarily joined to a metal bracket attached to a movable surface. The switch assembly contains a pivoted contact which moves against a fixed contact when the linearly movable element is displaced the predetermined distance. The contact remains there regardless of the subsequent position of the linearly moveable element until a button operationally connected to the switch assembly is moved to the off position. A problem with Nakada is that it does not include or combine with a bolt or lock. When significant force is applied to open the door or window, the magnetically retained holder 30 simply pulls free of metal bracket 34. Nakada offers only the attractive force of a small magnet against the brute strength of an intruder.
Blasucci, U.S. Pat. No. 4,206,452, issued on Jan. 3, 1980, discloses a tension cord burglar alarm. Blasucci includes web of tensioned cord secured to a window with suction cup fasteners. The web contains a switch activated by a change in cord tension, as might result from opening the window or from breaking through the window and pressing against the cords. A problem with Blasucci is that the suction cup fasteners could slip slightly relative to each other, change the cord tension and cause a false alarm. Another problem with Blasucci is that the cord offers no significant resistance to unauthorized opening of a window or door as a bolt or latch would.
It is thus an object of the present invention to provide a door and window securing combined alarm and latch apparatus which simultaneously locks the door or window and sets an alarm against unauthorized entry.
It is another object of the present invention to provide such an apparatus which permits partial opening of the door or window before the chain engages to stop further movement, sounding the alarm during this interval, so that the alarm sounds prior to intruder entry, giving building occupants and police greater response time.
It is finally an object of the present invention to provide such an apparatus which is strong, simple, reliable and relatively inexpensive to manufacture.